1. Field of the Invention
The present invention relates to an integrally molded type filter unit and a method for manufacturing the filter unit, more particularly to a filter unit possible to be produced by joining a filter holding frame to a separately produced filter part simultaneously with injection molding of the frame, installation easiness to be installed in a gas treatment apparatus, light weight and having low pressure loss and high dust collecting efficiency and to a manufacturing technique of the filter unit.
2. Description of the Related Art
Recently, the demand for a gas treatment apparatus such as an air purifier, an air conditioner equipped with such an air purifier, and the like has been increasing.
The gas treatment apparatus usually contains a filter for removing airborne dust and malodorous components. Such a filter is used as a filter unit comprising a filter part made of activated carbon-containing paper, polyester nonwoven cloths, glass fiber paper and formed in a sheet-like form or processed in a pleated form and a filter holding frame to which the filter part is attached. The filter unit is required to be easy for installation in a gas treatment apparatus.
Conventionally, in the case of manufacturing such a filter unit, a filter part previously processed to be a sheet-like shape or a pleated shape is made ready, built in a filter holding frame separately made ready and then fixed in the filter holding frame by methods, for example, by using an adhesive, engagement claws and screws, or springs. Consequently, there occurs a problem that the number of processes is high and the manufacturing efficiency is decreased.
Today, the following methods have been made known: as disclosed in Japanese Patent Unexamined Publication (Kokai) No. 10-263348, a method of integrally forming a filter unit using a packing in the circumference of a filter holding frame and as disclosed in Japanese Patent Unexamined Publication (Kokai) No. 11-90150, a method of using a foamed resin for a filter holding frame.
However, the methods aim at mainly improving the production efficiency but pay no attention to improvement of properties such as the strength and the weight of a filter unit itself and the capability and the characteristic as a filter.
An integrally molding method wherein a filter part made ready in a separated process is stuck to a filter holding frame simultaneously with the molding of the filter holding frame can be considered as a method for manufacturing a filter unit with a high strength and light weight at high manufacturing efficiency.
However, the integrally molding method also has a problem especially in the case where an adsorbent of such as an activated carbon is contained in a filter part. That is, the surface area of a filter part is widened to improve the function of an adsorbent even a little more, the joining part to a holding frame is lessened as much as possible to improve the dust collecting efficiency, and even the end part of a holding frame is filled with activated carbon to improve the filter molding processibility and such methods are considered to achieve such improvements, however these methods may possibly lead to burr formation or a damage on dies owing to separation of activated carbon from the end part of the filter material to a grip of the die.
Therefore, it can be considered to prevent burr formation and the damage of dies that no activated carbon is put in the end part of a filter material, however it causes a problem that the effective surface area as a filter is narrowed and the filter capability is decreased.
Further, it can also be considered to prevent burr formation and activated carbon separation that a resin flow-in part with a several mm width is formed in the grip part in the inner side of the frame by properly amending the die structure, however it causes a problem that the effective surface area as a filter is narrowed and the filter capability is decreased.
On the other hand, a filter holding frame for installing a filter in a gas treatment apparatus is desired to be excellent in handling flexibility as to be freely twisted or changed in the form at the time of installation and is preferable to be thin and light weight, however if the holding frame is made thin and light weight, the strength of the frame is decreased and it results in a problem that the frame is hard to be installed in a gas treatment apparatus, especially in a curved one.
The present invention hence aims at providing a filter unit having a wide effective surface area of a filtration material and capable of providing a high dust collecting efficiency without causing drop of the activated carbon from the end part of the filtration material of the filter to a grip part of dies and the present invention aims at providing a method for manufacturing such a filter unit.
The present invention further aims at providing a filter unit with light weight by making the thickness of the filter holding frame thin, excellent handling flexibility at the time of installation, a low pressure loss, and a high collecting efficiency and providing a method for manufacturing such a filter unit comprising an integrally molding process to simplify manufacturing processes and to lower the fraction defective in the manufacturing processes.
A filter unit according to the present invention is characterized by comprising a filter part made of an adsorbent-bearing filtration material and a filter holding frame made of a thermoplastic resin and integrally molded with a part of the filter part and the adsorbent of the filter part is packed to the position contacting the filter holding frame.
With such a constitution, a filter unit with a wide effective surface area of the filtration material and a high collection efficiency can be provided without causing burr formation or damages on dies owing to separation of the adsorbent, e.g. activated carbon, from the end part of the filtration material of the filter to a grip part of the die. Such a filter unit can be manufactured by a method, which will be described below, developed by inventors of the present invention.
The filter part in the present invention is a sheet-like or sheet-pleated product produced from paper, polyester or other polymer nonwoven cloths, glass fiber paper, porous resin sheets, various types of fabrics and textiles containing an adsorbent such as activated carbon, zeolites, and the like and subjected to the integrally molding process with a filter holding frame.
The materials for the filter holding frame to be employed for the present invention include thermoplastic resins such as acrylic resins, phenol resins, silicon resins, polyolefin resins, polyurethane resins, epoxy resins, polyester resins, poly(vinyl chloride) type resins, melamine resins, poly (vinyl acetate) type resins, polystyrene resins, and the like; thermoplastic elastomers such as styrene type thermoplastic elastomer, urethane type thermoplastic elastomer, olefin type thermoplastic elastomer, polyester type thermoplastic elastomer, polyamide type thermoplastic elastomer, vinyl chloride type thermoplastic elastomer, fluoro type thermoplastic elastomer, and the like; and any material which can be molded by molten injection molding.
The filter holding frame is preferable to have ribs in the side faces in the filtration material arrangement direction and the width of each rib is preferably 10 to 90% and more preferably 15 to 40% to the width of each side face in the filtration material arrangement direction of the filter holding frame. The thickness of each rib is preferably 10 to 70% and more preferably 20 to 50% to the thickness of each side face in the filtration material arrangement direction.
If the width of each rib is 10% or narrower to the width of the side faces of the holding frame, sufficient strength cannot be provided and hence it is not preferable. If the width is 90% or wider to the width of the side faces of the holding frame, the reinforcing effect can be provided, however it means that the side face thickness is thickened and that the holding frame cannot be light weight. By forming such ribs, as a practical example, in the case where the gap (the thickness) of the side faces (in the filtration material arrangement direction) of a filter holding frame of dies is controlled to be 2.005 mm or narrower, preferably 1.504 mm or narrower, the thickness of the side faces of a manufactured holding frame can be made to be 2 mm or thinner, preferably 1.5 mm or thinner.
In such a manner, even a resin such as an olefin type thermoplastic resin whose melt has a high viscosity can easily be injection-molded and the thickness of the side faces (in the filtration material arrangement direction, the width direction) of a filter holding frame can be thin and the installation easiness can be improved. Moreover, the degree to which the side faces (in the filtration material arrangement direction) of the filter holding frame is thinned can be compensated with the filter part to result in increase of the surface area of the filter part by the degree and consequently, the pressure loss can be lowered and the collection efficiency can be improved. Such a thin holding frame made of a thermoplastic resin, especially an olefin type thermoplastic elastomer, has not been made available before.
Further, the foregoing filter holding frame is preferable to have gates in 3 or more points in side faces in the filtration material arrangement direction. More preferably, gates are formed at 4 to 6 points.
Formation of the ribs and gates improves the fluidity of a melted resin at the time of injection molding and the melted resin is spread all over the dies within a short time and at the same time pressure is evenly applied to the whole gap of the dies to spread the resin without leaving any voids. As a result, a filter part positioned in the outlet side of the dies and the melted resin are almost perfectly brought into contact with each other without leaving any voids. Further, since the gap of the dies can be made narrow, the thickness of the produced filter holding frame can be thin. To be remarkable, the hardened resin is found reinforcing the side faces (filtration material arrangement direction) of the filter holding frame to significantly improve the strength of the produced filter and make the filter durable to the strain and impact.
The foregoing thermoplastic resin is preferably an olefin type thermoplastic elastomer. That is because the elastomer is especially excellent in impact durability and it is desirable.
A conventional method aims at improving the productivity by simplifying the processes and dies for filter holding frames are only for pouring a melted resin to the gap part of the dies, whereas the present invention provides a method developed based on investigation of the structure of dies to easily carry out injection molding of even a resin such as an olefin type thermoplastic elastomer whose melt viscosity is high, to thin the thickness of the side faces (in the filtration material arrangement direction and the width direction) of a filter holding frame, and to improve the installation easiness. Further, the degree to which the side faces (in the filtration material arrangement direction) of the filter holding frame is thinned can be compensated with the increase of a part of the filter and as a result, the pressure loss can be lowered and the collection efficiency can be improved.
Before, it has been said impossible to make a resin such as an olefin type thermoplastic elastomer, whose melt viscosity is high, thin in the thickness of the side faces (in the filtration material arrangement direction and the width direction) of a filter holding frame. A melted resin poured into dies from both sides in the filtration material width direction of the filter holding frame joins in the center part of the side faces (in the filtration material arrangement direction) of the filter holding frame. At that time, if the gap of the dies equivalent to rib parts is made thin, the short takes place at the time of the injection molding. The term, short, means that resin is not spread all over the dies for molding a filter holding frame and cooled and solidified while partially leaving voids and subsequently, causes uneven strength pattern and as a result partly defective parts are formed in the produced holding frame in the voids. However, owing to the formation of ribs, occurrence of the short is prevented and the inferior product production is decreased. Moreover, the strength of the whole body of a filter holding frame is increased and the filter holding frame is freely deformable at the time of installation and a problem of installation difficulty at the time of installing a filter holding frame in a curved gas treatment apparatus is solved. Without ribs and gates, a melted resin flows unevenly in the dies and uneven temperature distribution pattern is formed and subsequently cooling speed differs and an uneven strength pattern is formed in the side face parts of the cooled and solidified filter holding frame to result in short occurrence and inferior product formation.
The foregoing filter holding frame is preferable to have 1% or higher torsion defined as following equation:
torsion=[(L)/(W)]xc3x97100% 
(wherein, (L) denotes the distance in which a filter holding frame is moved owing to the strain when force is applied to the filtration material face in one end of the filter holding frame in the vertical direction while a side face in the opposed other end of the holding frame being fixed in the filtration material width direction; and (W) denotes the width of the holding frame).
The torsion is more preferably 10% or higher and furthermore preferably 25% or higher.
The twisting of a filter unit at the time of installing the unit in a gas treatment apparatus means the temporal deformation caused by the force applied to the filter unit at the time of insertion and the degree of the deformation is defined as the above-mentioned equation and represents the characteristic. That is, the torsion is defined as the value calculated by dividing the distance (L) in which a filter holding frame is moved owing to the strain when force is applied to the filtration material face in one end of the filter holding frame in the vertical direction while a side face in the opposed other end of the holding frame being fixed in the filtration material width direction with the width of the holding frame (W) and multiplying the obtained value by 100.
The smaller the torsion is, the tougher the holding frame is and the harder the holding frame is deformed and it means that installation in a curved gas treatment apparatus become more difficult. The torsion is sufficient to be at least 1% and in the case of 10% or higher, preferably 25% or higher, there is no trouble at the time of installation in a curved treatment apparatus.
The method for manufacturing a filter unit according to the present invention comprises a process of setting a filter part made of an adsorbent-bearing filtration material in dies, a process of pouring a thermoplastic resin in the dies in which the filter part is set and forming a filter holding frame integrally with the foregoing filter part.
The clearance A of an escape part in the foregoing dies is controlled to be 80 to 115% to the thickness of the foregoing filtration material, the clearance B in the grip part is controlled to be 25 to 45% to the thickness of the foregoing filtration material, and the distance C of the foregoing grip part is controlled to be 0.5 to 5 mm.
By controlling the clearance A of the escape part is controlled to be 80 to 115%, preferably 100 to 110%, the clearance B in the grip part is controlled to be 25 to 45%, preferably 35 to 40%, and the distance C of the grip part is controlled to be 0.5 to 5 mm, preferably 1 to 3 mm, the present invention can keep the surface area of the filtration material wide and provide an excellently integrally molded filter.
In this case, the clearance means the gap between dies sandwiching the filtration material part of the filter, that is, the distance between the cavity side and the core side. The grip part is positioned in the boundary of the filtration material of the filter to the holding frame and means another filtration material part of the filter, that is a part where the clearance is made narrow than the escape part. By forming the grip part and the escape part, a melted thermoplastic resin does not flow into the filtration material part and the filtration material structure can be formed without being damaged. Even if activated carbon is deposited in the filter terminal parts, the filter can easily be stuck to a holding frame by adjusting the A, B, C values and thus the present invention is completed.
With such a constitution, when a melted resin is poured to dies, bleeding of the melted resin to a filtration material does not take place and the filtration material of a filter can utilized to the utmost extent. If the clearance A is set 80% or lower, the filtration material of the filter is possibly pressurized and damaged and the pressure loss may be increased. If the clearance A is set 115% or higher, the pleated form of the filter part is possibly deformed and wrinkled. If the clearance B is set 25% or lower, too, the filtration material of the filter is possibly pressurized and damaged and the pressure loss may be increased. If the clearance B is set 45% or higher, the resin possibly flows out to the filter part and burrs may be formed. Further, if the distance C of the grip part is set 0.5 mm or shorter, too, the resin possibly flows out to the filter part and burrs may be formed and if the distance C is set 5 mm or longer, the surface area of the filter part is possibly decreased and the filtration capability is decreased and thus these are not preferable.